The system is ripe for an upheaval. Cheap online courses seem poised to deliver it. Traditional colleges at opposite ends of the glamour spectrum will probably survive. At one end, community colleges could deliver bankable skills in fields like nursing and computer network installation. At the other end, elite institutions like Princeton will carry on for a few more centuries.

“The U.S. higher education sector has hit a critical juncture in the evolution of its business model,” said Eva Bogaty, Moody’s assistant vice president, in a statement. “Even market-leading universities with diversified revenue streams are facing diminished prospects for revenue growth.”